Anadromous Fish

Historically, river herring runs into Connecticut rivers and streams numbered into the millions; however, runs have been declining steadily in recent decades. Recent restoration activities including, building fishways at dams, removing dams, and widening culverts, allow fish to bypass barriers to find habitat upstream to spawn, and thereby increase in abundance (counts at fish runs). In fact, as of 2022, these efforts have collectively reconnected 82 percent of potentially passable river miles. These restoration efforts may have assisted in slight population increases as seen in more recent years, but compounding factors beyond habitat connectivity may have negative impacts on these populations (see below).

Tracking anadromous fish populations can be an indicator of the Partnership’s efforts to reconnect riverine migratory corridors for the Habitat Connectivity Objective.

Blueback Herring and alewife

River herring is a collective term for the Blueback Herring, Alosa aestivalis, and Alewife, Alosa pseudoharengus, two anadromous fish species that can be found in the Long Island Sound watershed. Anadromous fish migrate from the ocean to rivers to spawn. River herring are important to our freshwater, marine, and estuarine ecosystems because adult herring and their young provide food for a variety of predators including freshwater gamefish, marine gamefish, ospreys, bald eagles, harbor seals, porpoises, egrets, kingfishers, and river otters.

Blueback Herring and Alewife possess traits suggestive of incredible resiliency. These traits include multiple spawning cycles for individual fish (i.e., dropping eggs at different times during a season) and staggering the population’s returns. Both traits enable the fish to overcome extreme environmental conditions like droughts and low flow. Additionally, habitat improvements with regards to habitat connectivity and water quality have been significant. Since 2014, the Partnership has connected over 140 river miles allowing for fish passage, and water quality improvements across the state have reduced nitrogen loads from wastewater treatment plants by over 58 percent. This reduction in nitrogen loads  contributed to significant reductions in the Sound’s total hypoxic area, which results in improved living conditions for fish. Despite these resiliency traits and habitat quality improvements, Blueback Herring and Alewife counts have not recovered and populations remain unstable.

Furthermore, populations are utilizing approximately only 4 percent of the capacity of our riverine corridors. The limited recovery of these species is thought to be due to overfishing. Recent population increases that coincided with a temporary pause and/or reduction in commercial fishing that occurred between 2023 and 2025 have further supported the link to overfishing.

• One of the greatest pressures Alewives face is over harvesting. Although Connecticut regulations prohibit Alewife and Blue Back Herring take, overharvesting persists in waters outside of Connecticut’s jurisdiction. River herring is caught as bycatch and incidental catch by commercial fleets targeting Atlantic herring and mackerel in Long Island Sound, as well as in other northeast estuaries and the Atlantic Ocean. When fleets catch river herring, they either discard them at sea (bycatch), or, since river herring closely resemble Atlantic herring, sell river herring as part of their herring catch (incidental catch) (NOAA Fisheries). This impact is believed to be a significant cause for declining herring populations at Bride Brook, as well as in other rivers and streams around Long Island Sound. The New England Fishery Management Council has drafted an Amendment to the Atlantic Herring Fishery Management Plan to address spatial and temporal allocation and management of Atlantic herring at the management unit level to minimize user conflicts, contribute to optimum yield, and support rebuilding of the resource. See the New England Fishery Management Council’s herring webpagefor more information.

American Shad

The American shad (Alosa sapidissima), an anadromous fish species related to the Blue Herring and Alewife, is the largest of Connecticut’s herring species. In 2003, the American shad was designated Connecticut’s “State Fish.” The 2007 American shad stock assessment found that most American shad stocks were at all-time lows and did not appear to be recovering. Since 2007, the observations of American shad in the Connecticut River have been variable and are not yet at a stable recovered population level.